Emission Features Research Articles

Doppler Tomography of the Be Star HD 698

We present a Doppler tomography study of the Be star HD 698, recently resolved via interferometry as a post-mass-transfer binary system consisting of a Be star and a stripped, pre-subdwarf companion. Based on 76 high-resolution optical spectra obtained between 2014 and 2023, we analyze the Hα and Hβ emission lines and apply Doppler tomography to map the structure of the circumstellar disk. The Hα line reveals an asymmetric, multi-component velocity distribution, with an emission feature closely following the orbital motion of the companion. V/R variations in both Hα and Hβ lines are phase-locked with the companion’s orbital motion, indicating a tidally induced disk asymmetry. We discuss possible origins of the companion-centered Hα emission, including a circumsecondary disk, a transient mass-transfer stream, and stellar wind.

Doping Bulky Fluorinated Organic Anion to Construct Highly Efficient Anion-π+ Type Photosensitizers for Cancer Phototheranostics.

Anion-π+ type photosensitizers with aggregation-induced emission (AIE) feature have demonstrated promising potential in photodynamic therapy (PDT) against cancer. However, previous reports mainly focused on modifying the π+ core but often overlooked the crucial role of anions. Herein, we present a facile strategy to modulate the fluorescence intensity and cellular uptake of anion-π+ type AIE photosensitizers by doping bulky fluorinated organic anions into nanoparticles (NPs). Anion-π+ type AIE photosensitizer DPBCF-Br with different ratios of bulky anions (TB or FTB) were encapsulated into DSPE-PEG2000 to obtain NPs (named DF-TBX or DF-FTBX, X denotes the molar ratios of TB or FTB to DPBCF-Br). Expectedly, as the doping molar ratios increased, a progressive enhancement in fluorescence intensity of the obtained NPs was observed. This can be ascribed to the steric effect of bulky organic anions and the formation of a hydrophobic environment within the NPs. Interestingly, the optimal cellular uptake was achieved at X=8 in DF-TB8 and DF-FTB8, resulting from the balance between lipophilicity and electronegativity. Ultimately, DF-FTB8 demonstrated outstanding cellular imaging capabilities and high intracellular reactive oxygen species generation, achieving efficient cancer phototheranostics. This facile bulky anion doping strategy will pave a new way for the construction of robust anion-π+ type photosensitizers.

Synthesis and Characterization of Polyaniline Emeraldine Salt: Tunable Photoluminescence and Optoelectronic Properties for Advanced Applications

Polyaniline emeraldine salt (PANI-ES) is a conductive polymer with promising optoelectronic properties, synthesized via chemical oxidative polymerization and confirmed in its emeraldine salt form through structural analysis. Optical characterization revealed distinct absorption bands linked to key electronic transitions, indicating semiconducting behavior. Under UV excitation, photoluminescence studies showed two main emission features corresponding to dimer and excimer states, both exhibiting large Stokes shifts and a quantum yield of 0.27. These long Stokes shifts suggest efficient energy relaxation, while the moderate quantum efficiency highlights the material’s capability for light-emitting applications. The combination of tunable emission, stable optical response, and electrical conductivity positions PANI-ES as a versatile material for photonic technologies. Potential applications include organic light-emitting diodes (OLEDs), photodetectors, and optically pumped organic lasers. Overall, the study demonstrates that PANI-ES offers a favorable balance of structural stability, optical performance, and electronic properties, making it a strong candidate for integration into advanced optoelectronic and photonic devices.

Modulation of up-conversion luminescence properties by poling and Er3+ doping of KNN-based ceramics

Perovskite oxides with luminescent ions hold great promise in optoelectronic devices because of their outstanding thermal stability and electro-optic performance. In this work, 0.95K[Formula: see text]Na[Formula: see text]Nb[Formula: see text]Sb[Formula: see text]O3-0.05Bi[Formula: see text]Na[Formula: see text]ZrO[Formula: see text] mol Er[Formula: see text] (KNNS-BNZ-xEr) ceramics were synthesized using the traditional solid-state method. Effects of Er[Formula: see text] content on the phase structure, microstructure and photoluminescent properties of the ceramics were investigated. The introduction of rare-earth Er[Formula: see text] improved the lattice symmetry, refined the grain size and endowed the ceramics with photoluminescent properties. The ceramics show bright green emission and red emission under 980[Formula: see text]nm stimulation at room temperature. The maximum luminescence intensity was reached at [Formula: see text]. Additionally, luminescence emission intensity can be easily modulated by poling. It is found that the KNNS-BNZ-0.01Er ceramics with the optimal UC emission features show the highest luminescence intensity contrast ([Formula: see text]) value of 3.02 after poling. It was found that the poling modulation of luminescence was closely related to cell distortion and band structure. These findings provide valuable insights for the development of KNN-based ceramics in optical applications such as luminescence switching.

Experimental and computational insights into the electronic structures and absorption-emission characteristics of coumarin, C-6H, C-153, and C-343 dyes.

Experimental and computational insights into the electronic structures and absorption-emission characteristics of coumarin, C-6H, C-153, and C-343 dyes.

Optical properties of Zr-doped AlN epilayers

Aluminum nitride (AlN) doped with zirconium (Zr), AlN:Zr, an ultrawide bandgap semiconductor, has been theoretically predicted as a promising material for quantum information systems, piezoelectric applications, and photoconductive semiconductor switches. We report on the optical characterization of AlN:Zr epilayers synthesized by metal-organic chemical vapor deposition. Photoluminescence measurements demonstrate that Zr doping introduces distinct emission features near 1.8, 2.46, and 3.63 eV. These emission lines, together with a prominent absorption peak centered at 1.78 eV whose intensity increases with Zr content, are identified as originating from the complex between Zr and nitrogen vacancy, ZrAl–VN. Evidence indicates that the dominant optical absorption and emission pathways involve the neutral charge state of this complex, (ZrAl–VN)0. This finding is highly encouraging, given that (ZrAl–VN)0 is considered an ideal candidate for a qubit. Concurrently, our analysis reveals that Zr incorporation also promotes the formation of deleterious aluminum vacancy (VAl) and VAl-complex related defects, necessitating process optimization to minimize their concentration for practical device realization.

Inferring chromospheric velocities in an M3.2 flare using He I 1083.0 nm and Ca II 854.2 nm

Aims. Our aim was to study the chromospheric line-of-sight (LOS) velocities during the GOES M3.2 flare (SOL2013-05-17T08:43) using simultaneous high-resolution ground-based spectroscopic data of the He I 10830 Å triplet and Ca II 8542 Å line. A filament was present in the flaring area. Methods. The observational data were acquired with the Vacuum Tower Telescope (VTT, Tenerife, Spain) and covered the pre-flare, flare, and post-flare phases. Spectroscopic inversion techniques (HAZEL and STiC) were applied individually to He I and Ca II lines to recover the atmospheric parameters of the emitting plasma. Different inversion configurations were tested for Ca II, and two families of solutions were found to explain the red-asymmetry of the profiles: a redshifted emission feature or a blueshifted absorption feature. These solutions could explain two different flare scenarios (condensation vs. evaporation). The ambiguity was solved by comparing these results to the He I inferred velocities. Results. At the front of the flare ribbon, we observed a thin short-lived blueshifted layer. This is seen in both spectral regions, but is much more pronounced in He I, with velocities of up to −10 km s−1. In addition, at the front we found the coexistence of multiple He I profiles within one pixel. The central part of the ribbon is dominated by He I and Ca II redshifted emission profiles. A flare-loop system, visible only in He I absorption and not in Ca II, becomes visible in the post-flare phase and shows strong downflows at the footpoints of up to 39 km s−1. In the flare the Ca II line represents lower heights compared to the quiet Sun, with peak sensitivity shifting from log τ≃−5.2 to log τ≃−3.5. The loop system's downflows persist for over an hour in the post-flare phase. Conclusions. The inferred LOS velocities support a cool-upflow scenario at the leading edge of the flare, with rapid transition from blueshifts to redshifts likely to occur within seconds to tens of seconds. Although the flare had a significant impact on the surrounding atmosphere, the solar filament in the region remained stable throughout all flare phases. The inclusion of the He I triplet in the analysis helped resolve the ambiguity between two possible solutions for the plasma velocities detected in the Ca II line. This highlights the importance of combining multiple chromospheric spectral lines to achieve a more comprehensive understanding of flare dynamics.

The birth of Be star disks

Context. Classical Be stars are well known to eject mass to build up a disk, but the details governing the initial distribution and subsequent evolution of this matter into a disk are in general poorly constrained through observations. Aims. By combining high-cadence time-series spectroscopy with contemporaneous space photometry from the Transiting Exoplanet Survey Satellite (TESS), we have sampled about 30 mass ejection events in 13 Be stars. Our goal is to constrain the geometrical and kinematic properties of the ejecta as early as possible, facilitating the investigation into the material's initial conditions and evolution, and understanding its interactions with preexisting material. Methods. The photometric variability is analyzed together with measurements of the at-times rapidly changing emission features in order to identify the onset of outburst events and obtain information about the geometry of the ejecta and how it changes over time. Short-lived line asymmetries display oscillation cycles (Štefl frequencies), which are compared to photometric and stable spectroscopic frequencies. Results. All Be stars observed with sufficiently high cadence during an outburst are found to exhibit rapid oscillations of line asymmetry with a single frequency in the days following the start of the event. For a given star this circumstellar frequency may differ only slightly from event to event even when the outbursts they are associated with have different properties. These circumstellar frequencies are typically between 0.5 to 2 d−1, and are generally near photometric frequencies. They are slightly below prominent (generally stable) spectroscopic frequencies seen in photospheric absorption lines. The emission asymmetry cycles break down after roughly 5–10 cycles, with the emission line profile converging toward approximate symmetry shortly thereafter. In photometry, several frequencies typically emerge at relatively high amplitude at some point during the mass ejection process. Conclusions. In all observed cases, freshly ejected material was initially constrained within a narrow azimuthal range, indicating it was launched from a localized region on the stellar surface. The material orbits the star with a frequency consistent with the near-surface Keplerian orbital frequency. This material circularizes into a disk configuration after several orbital timescales. This is true whether or not there was a preexisting disk at the time of the observed outburst. We find no evidence for precursor phases prior to the ejection of mass in our sample. The several photometric frequencies that emerge during outburst are at least partially stellar in origin.

A Data-Driven Method for Deriving the Dynamic Characteristics of Marginal Carbon Emissions for Power Systems

Understanding the dynamic carbon emission status is vital for turning a power system into a low-carbon system. However, the existing research has normally considered the average carbon emissions as the indicator for the operation and planning of power systems. Detailed carbon emission responsibility is not well allocated to different demands within power systems, leading to inefficient emission control. To address this problem, this paper develops a data-driven method for accurately finding the characteristics of the nodal marginal emission factor without the requirement of real-time optimal power flow (OPF) simulation. First, the nodal marginal emission factor system is derived based on actual data covering a timespan of one year on top of the IEEE 118 system. Then, a Graphical Neural Network (GNN) is adopted to map both the spatial and temporal relationship between nodal marginal emission and other features, thereby identifying the marginal emission characteristics for different nodes of power transmission systems. Through case studies, fine-tuned GNNs estimate all nodal marginal emission factor (NMEF) values for power systems without the requirement of OPF simulation and achieve a 5.75% Normalized Root Mean Squared Error (nRMSE) and 2.52% Normalized Mean Absolute Error (nMAE). Last but not least, this paper brings a new finding: a strong inclination to reduce marginal emission rates would compromise economic operation for power systems.

Room temperature photoluminescence revival of pulsed laser deposition grown few-layer WS2 thin films

Abstract The intricate competition between seed formation and the growth-limited area in 2D transition metal dichalcogenides has long hindered their potential applications. This study investigated the morphological and photophysical characteristics of few-layer tungsten disulfide (FL-WS2) thin films deposited on SiO2/Si substrates via pulsed laser deposition (PLD). To induce morphological changes, the number of laser pulses was varied (50, 150, and 300 shots), followed by a post-deposition annealing treatment. Atomic force microscopy (AFM) demonstrated three distinct morphological features: continuous films, particulates, and islands, indicative of a growth evolution consistent with the Stranski–Krastanov (layer-plus-island) mechanism. X-ray photoelectron spectroscopy (XPS) revealed the presence of a semiconducting phase of 2H-WS2 and sulphur-deficient species (WSx) in the films. While Raman modes characteristic of WS2 were observed, the absence of photoluminescence (PL) emission suggested the presence of defect states in the as-grown thin films. Upon post-annealing treatment, we observed a reduction in WSx species (150 and 300 laser shots) accompanied by a reduction of particulate density. This, in turn, triggers a defect state suppression, by which the PL spectra of all samples emerge, unveiling the near-resonance emission and excitonic features. This observation was confirmed by the density functional theory (DFT) simulation, pointing to the presence of an extra energy level around the K point of the Brillouin zone at high concentration of sulphur vacancy, which corresponds to the splitting of near-resonant PL emission. In addition, two pronounced Raman modes at 264 cm−1 and 334 cm−1 are associated with structural relaxation due to post-annealing. This relationship between morphological characteristics and emissive behaviour of large-area FL-WS2 thin films provides valuable insights into their photophysical modulation, paving the way for advanced photonic applications.

Dual-Center Emitting Pacs-MOF⊇Dye Composite Material Featuring Stimuli-Responsive Luminescence-Tuning Behavior for Information Encryption.

To satisfy the rising requirement for luminescence anticounterfeiting technology, the development of luminescent materials with multiple modes of emission and adjustable luminescence properties is essential. On account of the great structural programmability of luminescent metal-organic frameworks (LMOFs), the multiple emitting components can be integrated into the matrices of LMOFs and form the multicentered synergistic emission system; thus, LMOFs can be an ideal platform for fabricating luminescent anticounterfeiting materials. Herein, based on the pore space partition (PSP) strategy, a novel pacs-MOF Mg-TPA-bdc with the formula of {(NH2Me2)[Mg3(μ3-OH)(bdc)3(TPA)]·12H2O}n (TPA = Tri(pyridin-4-yl)amine; bdc = terephthalic acid) was constructed as a host matrix to encapsulate the acriflavine during the self-assembly process to construct a new dual-centered emission material Mg-TPA-bdc⊇AF, which exhibited blue and green emission under 365 and 460 nm excitation, respectively. Intriguingly, upon external pressure or temperature variation, both of these two materials exhibit reversible stimuli-responsive luminescence-tuning behavior, which can be observed by the naked eye. Considering the charming dual-centered emission features of Mg-TPA-bdc⊇AF, a novel binary-coded microarray data storage matrix with high security reliability, real-time response, and great reversibility was constructed and applied for information encryption and luminescence anticounterfeiting.

MINDS: The very low-mass star and brown dwarf sample. Detections and trends in the inner disk gas

Planet-forming disks around brown dwarfs and very low-mass stars (VLMS) are, on average, less massive and are expected to undergo faster radial solid transport than their higher-mass counterparts. Spitzer had detected C_2H_2 CO_2 and HCN around these objects but did not provide a firm detection of water. With a better sensitivity and spectral resolving power than that of Spitzer the James Webb Space Telescope (JWST) has recently revealed incredibly carbon-rich spectra and only one water-rich spectrum from such disks. A study of a larger sample of objects is necessary to understand how common such carbon-rich inner disk regions are and to put constraints on their evolution. We present and analyze JWST MIRI/MRS observations of ten disks around VLMS from the MIRI guaranteed time observations program. This sample is diverse, with the central object ranging in mass from 0.02 to 0.14 M_⊙. They are located in three star-forming regions and a moving group (1 to 10,Myr). We identified molecular emission in all sources based on recent literature and spectral inspection, and reported detection rates. We compared the molecular flux ratios between different species and to dust emission strengths. We also compared the flux ratios with the stellar and disk properties. The spectra of these VLMS disks are extremely rich in molecular emission, and we detect the 10,μm silicate dust emission feature in 70% of the sample. We detect C_2H_2 and HCN in all the sources and find larger hydrocarbons, such as C_4H_2 and C_6H_6 in nearly all sources. Among oxygen-bearing molecules, we find firm detections of CO_2 H_2O and CO in 90%, 50%, and 20% of the sample, respectively. We find that the detection rates of organic molecules correlate with other organic molecules and anticorrelate with the detection rates of inorganic molecules. Hydrocarbon-rich sources show weaker 10,μm dust strengths, as well as lower disk dust masses (measured from millimeter fluxes) than the oxygen-rich sources. We find evidence for a C/O ratio enhancement with disk age. The observed trends are consistent with models that suggest rapid inward solid material transport and grain growth.

Two-Dimensional Materials as Ideal Substrates for Molecular Quantum Emitters.

The generation and manipulation of nonclassical states of light is central to quantum technologies. Color centers in insulators have been extensively studied for single-photon generation, but organic molecules immobilized on substrates have gained attention due to their superior scalability, large oscillator strengths, and tunable emission frequency. Here, we use first-principles calculations to investigate the photoemission from organic molecules adsorbed on 2D materials. Focusing on terrylene on hexagonal boron nitride (hBN), we obtain zero phonon line (ZPL) energies and emission lineshapes in excellent agreement with experiments. Notably, antisite defects in hBN can immobilize the molecule without influencing its key emission features. We further show that the main effect of the 2D substrate is to introduce sharp sidebands near the ZPL as a fingerprint of hindered rotational, translational, or bending modes of the molecule. Our findings provide insight into how substrate interactions shape the optical properties of molecular systems for quantum applications.

The S-PLUS Fornax Project (S+FP): Mapping Halpha+[N II] emission in 77 Fornax galaxy members reaching ∼4 Rvir

The Fornax cluster, the second-largest galaxy cluster within 20 Mpc, presents an ideal environment for studying the impact of environmental effects on galaxy evolution. Utilizing data from the Southern Photometric Local Universe Survey (S-PLUS), this study explores the emission maps in Fornax and its outskirts. By mapping emission features across an area of approximately 208 square degrees around NGC 1399, this work aims to identify and characterize emission-line galaxies (ELGs) and analyze their spatial distribution, morphology, and their projected phase space (PPS) diagram. We developed a dedicated semiautomated pipeline, pixel-to-pixel emission line estimate (PELE), to generate emission line maps by processing S-PLUS images using the three-filter method. A morphological analysis was conducted using the ASTROMORPHLIB package to determine whether emitters exhibit perturbed features. The study successfully detected 77 emitters with r_ AB <18 mag, extending to four times the virial radius of the Fornax cluster. PELE demonstrated its ability to recover flux down to ∼2 erg s^-1 cm^-2 when compared to Hα maps from MUSE/VLT. Among the emitters, 25% are early-type galaxies (ETGs) and 75% are late-type galaxies (LTGs). Signs of morphological perturbation or merger activity are observed in 44% of the LTGs and in three ETGs located beyond the cluster’s virial radius. A significant fraction (91%) of the emitters are identified as recent infallers, which are primarily located in the northwestern region of the cluster, while others are associated with the infalling group Fornax,A in the southwest. Disturbed, low-mass galaxies at larger cluster-centric distances provide evidence that galaxies begin transforming before entering the main cluster. This study demonstrates S-PLUS’s effectiveness in detecting ELGs, whose distribution reflects the Fornax cluster’s assembly history; LTGs are linked to recent infall from the field, possibly along a Fornax-Eridanus filament, and ETGs may have evolved prior to entry.

From Pretransit to Posteclipse: Investigating the Impact of 3D Temperature, Chemistry, and Dynamics on High-resolution Emission Spectra of the Ultrahot Jupiter WASP-76b

Abstract High-resolution spectroscopy has provided a wealth of information about the climate and composition of ultrahot Jupiters (UHJs). However, the 3D structure of their atmospheres makes observations more challenging to interpret, necessitating 3D forward-modeling studies. In this work, we model phase-dependent thermal emission spectra of the archetype UHJ WASP-76b to understand how the line strengths and Doppler shifts of Fe, CO, H2O, and OH evolve throughout the orbit. We postprocess outputs of the SPARC/MITgcm global circulation model with the 3D Monte Carlo radiative transfer code gCMCRT to simulate emission spectra at 36 orbital phases. We then cross correlate the spectra with different templates to obtain cross-correlation function and K p–V sys maps. For each species, our models produce consistently negative K p offsets in pre- and posteclipse, which are driven by planet rotation. The size of these offsets is similar to the equatorial rotation velocity of the planet. Furthermore, we demonstrate how the weak vertical temperature gradient on the nightside of UHJs mutes the absorption features of CO and H2O, which significantly hampers their detectability in pre- and posttransit. We also show that the K p and V sys offsets in pre- and posttransit are not always a measure of the line-of-sight velocities in the atmosphere. This is because the cross-correlation signal is a blend of dayside emission and nightside absorption features. Finally, we highlight that the observational uncertainty in the known orbital velocity of UHJs can be multiple kilometers per second, which makes it hard for certain targets to meaningfully report absolute K p offsets.

Near-Infrared AIE Probe for Cancer Cell Imaging and Therapeutic Applications.

Near infrared (NIR) aggregation-induced emission (AIE)-based luminogens are emerging as powerful materials with significant potential in cancer diagnosis, imaging, and therapy applications. Of precise note are the rapidly progressing areas in the field encompassing deep-tissue imaging, resistance to photobleaching, and biomedicine. Unlike traditional aggregation-caused quenching (ACQ) fluorophores, AIE materials with NIR emissive features can revolutionize the broad transdisciplinary areas of biomedicine, therapy, and healing, making them highly effective for real-time monitoring and healthcare purposes. In this study, we have synthesized a (E)-2-(2-(4'-(2,2-diphenylvinyl)-[1,1'-biphenyl]-4-yl)vinyl)-1,3,3-trimethyl-3H-indol-1-ium, named as 3T, and explored its antiproliferative potential on MCF-7 and MDA-MB-231 breast cancer cells. The 3T molecule exhibited strong near-infrared (NIR) emission ranging from 600 to 800 nm in a 99% water fraction (fw). In silico target prediction and molecular docking identified potential target proteins and assessed their binding interactions and affinities. Further, in vitro studies demonstrated efficient cellular internalization and dose-dependent reduction in cell viability. The IC50 values of 32.26 and 35.75 μM were observed in MCF-7 and MDA-MB-231 cells, respectively. The treatment of 3T generated 2.1- and 1.9-fold increases in reactive oxygen species (ROS) for MCF-7 and MDA-MB-231 cells, respectively, and induced a change in mitochondrial membrane potential, leading to apoptosis, as confirmed by flow cytometry studies. The treatment was also effective for tumor spheroids. Thus, NIR AIEgen 3T offered several distinct advantages such as strong antiproliferative ability, stability, and imaging, positioning it as a potential candidate for cancer therapeutic applications.

SN 2022acko: a low-luminosity SNe IIP with signs of early circumstellar interaction

ABSTRACT We present optical-ultraviolet photometry and optical spectra for the type II supernova (SN) 2022acko. The spectroscopic observations span phases from $\sim$1.5 to $\sim$60 d after the explosion, while the light curve was observed up to $\sim$300 d. The V-band peak is $-15.5 \pm 0.3$ mag, suggesting that SN 2022acko is a low-luminosity SN II (LLSN). The overall observed properties of SN 2022acko are consistent with those produced by a lower mass progenitor ($\rm M_{ZAMS} \sim$9–10 M$_{\odot }$). The spectra at $t=1.5$ d and $t=2.5$ d exhibit a broad emission feature peaking near 4600 Å (the ‘ledge’ feature), which we interpret as blueshifted He ii 4686 Å lines arising from the ionized ejecta. Moreover, a possible flash-ionized (FI) emission line of H$\alpha$ (FWHM $\sim 1100\ \rm km \ s^{-1}$) was superposed on the broad emission component of H$\alpha$ P-Cgyni profile in the $t=1.5$ d spectrum. Assuming an ejecta velocity of $\rm 12000\ km\ s^{-1}$, the rapid disappearance of this narrow H$\alpha$ emission line within 2 d suggests highly confined circumstellar material (CSM) within $\sim \rm 2\times 10^{14}\, cm$. Assuming a spherically symmetric CSM, the mass loss rate within this radius is estimated to be $\rm \sim 5 \times 10^{-4} {\rm M}_{\odot } \ yr^{-1}$ based on our hybrid light curve model. The early ‘ledge’ feature observed in SN 2022acko have also been observed in other SNe II, suggesting that early-phase circumstellar interaction is more common than previously thought.

21 cm signal from dark-age collapsing halos with a detailed molecular cooling treatment

Context. To understand the formation of the first stars, a detailed description of the thermal and chemical processes in collapsing gas clouds is essential. Molecular cooling, particularly via H2, plays a significant role in triggering thermal instabilities that lead to star formation. The 21 cm hydrogen line serves as a potential probe of the first collapsing structures during the dark ages of the early Universe and it is affected by the gas temperature evolution. Aims. We aim to investigate the molecular cooling in the gas halos prior to the formation of the first stars, with a particular focus on how the H2 cooling affects the gas temperature. Additionally, we explore the sensitivity of the 21 cm hydrogen line to these cooling processes during the collapse of the first overdense regions. Results. We introduce the CHEMFAST code, which tracks the evolution of chemical abundances and computes the 21 cm neutral hydrogen signal in collapsing halos. Our results show that molecular cooling significantly affects the gas temperature inside collapsing clouds of mass ranging from 106 to 109 M⊙, influencing the 21 cm signal. The signal exhibits an emission feature that is distinct from the one predicted in simpler expansion models. Conclusions. The 21 cm brightness temperature inside collapsing clouds displays an emission feature driven by molecular cooling, closely mirroring the gas temperature evolution. This makes the dark-age 21 cm signal a promising probe for studying the thermal processes and structure formation in the early Universe.

JWST MIRI reveals the diversity of nuclear mid-infrared spectra of nearby type 2 quasars

Type 2 quasars (QSO2s) are active galactic nuclei (AGN) seen through a significant amount of dust and gas that obscures the central supermassive black hole and the broad-line region. Here, we present new mid-infrared spectra of the central kiloparsec of five optically selected QSO2s at redshift z ∼ 0.1 obtained with the Medium Resolution Spectrometer module of the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST). These QSO2s belong to the Quasar Feedback (QSOFEED) sample, and they have bolometric luminosities of log Lbol = 45.5 to 46.0 erg s−1, global star formation rates (SFRs) that place them above the main sequence, and practically identical optical spectra in terms of spectral shape and [OIII] luminosity, but their nuclear mid-infrared spectra exhibit an unexpected diversity in both continua and features. They show 9.7 μm silicate features going from emission (strength of S9.7 = 0.5) to relatively strong absorption (S9.7 = –1.0), and 18 and 23 μm silicates that are either in emission or flat (S18 = [0.2,0.0] and S23 = [0.1,0.0]). In addition, two of the QSO2s show absorption bands of CO, H2O, and aliphatic grains, indicating different levels of nuclear obscuration across the sample. Their [NeV]/[NeII] ratios range from 0.1 to 2.1 and [NeIII]/[NeII] from 1.0 to 3.5, indicating different coronal line and ionizing continuum strengths. They have warm molecular gas masses of 1–4 × 107 M⊙ and warm-to-cold gas mass ratios of 1–2%, with molecular gas excitation likely due to jet-induced shocks in the case of the Teacup (J1430+1339) and to UV heating and/or turbulence in J1509+0434. Finally, they show polycyclic aromatic hydrocarbon (PAH) emission features with equivalent widths ranging from less than 0.002 to 0.075 μm, from which we measure a larger contribution from neutral molecules (PAH 11.3/6.2 = 1.3–3.4) and SFRs ≤ 3–7 M⊙ yr−1. This unprecedented dataset allowed us to start exploring the role of various AGN and galaxy properties, including ionizing continuum, obscuration, electron density, and jet-interstellar medium interactions, in some of the spectral differences listed above. Larger samples observed with JWST/MIRI are now required to fully understand the diversity of QSO2s’ nuclear mid-infrared spectra.

Methane emissions features from China's municipal wastewater management, based on the whole-process evaluation of collection, treatment and discharge

Methane emissions features from China's municipal wastewater management, based on the whole-process evaluation of collection, treatment and discharge